The time dependent phenomena which accompany spontaneous vasomotor activity in arterioles will be studied in the skin flap window chamber preparation of the hamster. The diameter of active arterioles will be measured as a function of time by means of the image shearing video monitor. The red blood cell velocity of arterioles and the capillaries which originate from an active arteriole will be measured by means of dual window optical and video photometric technique. The data will be characterized in terms of amplitude and frequency of the effects and related to the local anatomical configuration and distribution of the vessels in which the effects take place. The ultimate objectives are to characterize tissue perfusion and the exchange of fluid between blood and tissue compartments in terms of the time dependent effects which we hypothesize are operative as a consequence of the rhythmic and continuous changes of caliber of the arteriolar circulation.